The closest relatives of the Red-spotted Purple Butterfly, Limenitis arthemis are Admiral butterflies that take their name from a solid white bar on the forewing. The Red-Spotted Purple has two color types, the mimetic Red-spotted Purple and the cryptic White Admiral. The bar helps camouflage Admiral Butterflies from birds as the white bar breaks up the outline of the butterfly wings. The Red-spotted Purple Type, with its Blue-black Purplish hue and red spots mimics the toxic Pipevine Swallowtail. The Red-spotted Purple lost the white stripe of its Admiral relatives as it evolved into a mimic of Pipeline Swallowtails (which have no white stripe). The mimicry provides useful protection against potential predators in areas where the population overlaps with the Pipevine Swallowtail.
The Pipevine Swallowtail is toxic because it feeds on plants in the family Aristoloceacea (such as Dutchman’s Pipe) that contain intensely bitter and toxic aristolochic acids. The Pipevine swallowtail can be found in Tippecanoe County, Indiana, but its range is mostly to the south where host plants are more abundant. The Red-spotted Purple can feed on a variety of plants that extend farther north outside the range of its protective model, the Pipevine Swallowtail. As Pipevine swallowtail becomes less frequent, the Red-spotted Purple color type becomes less frequent and is replaced by the White Admiral color type. White Admirals are more common in northern portions of its range such as New England, where the mimicry is less adaptive.
Genetic analysis suggests* that the White Admiral is descended from the Red-spotted Purple. The mimicry allowed the Red-spotted purple to become a successful species, but when its range extended outside the mimicry zone, it reverted back to a white stripe and cryptic defensive strategy.
*Kathleen L Prudic, Jeffrey C Oliver. 2008. Once a Batesian mimic, not always a Batesian mimic: mimic reverts back to ancestral phenotype when the model is absent. Proc. R. Soc. B 2008 275 1125-1132;